AWE-somes: All Water Emulsion Bodies Formed by Polyelectrolytes at Interfaces
Abstract: Interfaces between fluids are rich environments to trap materials and build films. Particles and molecules adsorb at interfaces to lower the interfacial energy and so can be collected from bulk fluid phases to form interfaces covered with monolayer or multilayer structures. This system is an excellent platform for capsule formation. By placing droplets in an external phase, materials from either the dispersed or continuous phases can be incorporated into films. Judicious selection of these components can lead to highly versatile, tailored structures.
We are developing encapsulation methods via interfacial complexation of polyelectrolytes and other charged species in all aqueous two phase systems to make multifunctional all-water emulsion bodies (AWE-somes). Such capsules might be particularly interesting for sequestration of delicate components, including proteins and microbes, which should not be placed in contact with oils or hydrophobic media.
Here we discuss the example of the PEG-Dextran-water system, which separates into PEG-rich and dextran-rich phases. The interfacial tension between the phases is quite low. Furthermore, many molecules, including polyelectrolytes, partition freely between the two phases. These factors make interfacial structure formation especially challenging. We develop strategies to build membranes from complementary polyelectrolytes in each phase by balancing their rates of transport to the interface. To impart additional functionality, we develop methods to include charged nanoparticles in such membranes. Here, nanoparticles can be selected that preferentially partition into one of the phases, facilitating interfacial transport, and creating an osmotic imbalance that leads to spontaneous formation of encapsulated multiple emulsions. These AWE-somes, with internal structures reminiscent of membraneless organelles in cells, provide a rich platform for separation, partitioning, reaction, and transport, suggesting AWE-somes might be developed into capsules that mimic biological cell functions or protocell systems.